1. Field of the Invention
The invention is generally related to the area of optical communications. In particular, the invention is related to a method and apparatus for regulating optical channel signals with specified wavelengths.
2. The Background of Related Art
The future communication networks demand ever increasing bandwidths and flexibility to different communication protocols. DWDM (Dense Wavelength Division Multiplexing) is one of the key technologies for such optical fiber communication networks. DWDM employs multiple wavelengths or channels in a single fiber to transmit in parallel different communication protocols and bit rates. Transmitting several channels in a single optical fiber at different wavelengths can multi-fold expand the transmission capacity of the existing optical transmission systems, and facilitating many functions in optical networking.
In general, each of the channel signals comes from a different source and may have transmitted over different mediums, resulting in a different power level. Without equalizing the power levels of the channel signals that are to be combined or multiplexed, some channels in a multiplexed signal may be distorted as a result of various stages of processing the multiplexed signal. On the other hand, many optical devices or systems would not function optimally when incoming signals are beyond a predetermined signal level range. In fact, the power of the incoming signals shall not be too low, neither too high. To ensure that all optical devices or systems receive proper levels of optical signals, attenuation devices are frequently used to adjust the optical signals before they reach an optical device.
Many existing optical attenuation devices lack accuracy and have high feedback noise. For example, screws are often used to intrude in an optical path to disrupt or cause to reflect some of the energy in a light beam not to reach a destination so that the light beam may be attenuated. However, in practical application, it is noticed that such attenuation is hard to be controlled. Because every time, a screw is rotated either upwards or downwards, the attenuation is not monotonically changed. This is particularly related to the surface changes of the screw. Unless the tip of a screw is made perfect, the circumambiency of the tip of the screw often has some variances, which resulting in non-monotonic changes in attenuation when the screw is caused to move up and down. Although a perfect screw may be made, the eventual cost of the attenuator may not be practical. Therefore there is a need for cost-effective attenuators with monotonic attenuation.